A fluoroaryl magnesium derivative, which is a Grignard reagent, is well known, for example, as an excellent reactant (organic synthetic reagent) for introducing a fluoroaryl group into various kinds of organic compounds. Also, in recent years, the fluoroaryl magnesium derivative has been receiving considerable attention as a synthetic material of a tris(fluoroaryl)borane compound serving as an excellent cocatalyst for a metallocene catalyst (polymeric catalyst).
A process for preparing a fluoroaryl magnesium derivative is disclosed, for example, in J. Org. Chem., 29, 2385 (1964). More specifically, an alkyl magnesium derivative, such as ethyl magnesium bromide (EtMgBr), is dropwise to a solution prepared by dissolving pentafluorobenzene into an ether solvent, such as tetrahydrofuran (THF). Consequently, a pentafluorophenyl magnesium derivative is obtained as the fluoroaryl magnesium derivative. Japanese Laid-open Patent Application No. 247976/1994 (Tokukaihei 6-247976) discloses another process. In this process, the pentafluorophenyl magnesium derivative is obtained by adding a solution prepared by dissolving pentafluorobenzene into an ether solvent to another solution prepared by mixing an alkyl magnesium derivative with the ether solvent.
In these processes, the pentafluorophenyl magnesium derivative is obtained through an exchange reaction, in which an alkyl group in the alkyl magnesium derivative is replaced with a pentafluorophenyl group.
However, in these processes, the alkyl magnesium derivative is produced before the above exchange reaction is carried out to obtain the pentafluorophenyl magnesium derivative. In other words, since the alkyl magnesium derivative is prepared separately before obtaining the pentafluorophenyl magnesium derivative, the reaction takes place in two steps.
To solve the above problem, the present invention has a first object to provide a process for producing the fluoroaryl magnesium derivative efficiently at a low cost in a simple manner virtually in a single step reaction.
A (fluoroaryl)borane compound, particularly, tris(pentafluorophenyl)borane, is known, for example, as an excellent cocatalyst for promoting the activity of a metallocene catalyst (polymeric catalyst) used in a cation complex polymerization reaction, and recently, the metallocene catalyst has been receiving considerable attention as a polyolefin polymerization catalyst.
An example process of obtaining the above-mentioned tris(pentafluorophenyl)borane is disclosed in Proc. Chem. Soc., 1963 (July), 212. More specifically, pentafluorobenzene lithium produced by reacting bromopentafluorobenzene and butyl lithium is reacted with boron trichloride, and as a consequence, tris(pentafluorophenyl)borane is obtained. However, in this process, the reaction system must be cooled to 78.degree. C., which makes this process almost inapplicable for industrial use.
To solve the above problem, a process using the Grignard reaction is disclosed in Z. Naturforsch., 20b, 5 (1965) as another example process of obtaining the tris(pentafluorophenyl)borane. According to this process, for example, pentafluorophenyl magnesium bromide and boron trifluoride diethyl etherate are reacted with each other in a chain ether solvent. Thus, it is not necessary to cool the reaction system to -78.degree. C., which makes this process advantageous over the above-mentioned reaction. Further, Japanese Laid-open Patent Application No. 199871/1994 (Tokukaihei 6-199871) discloses a process of obtaining triarylborane by reacting an aryl magnesium halide derivative and boron halide in a chain ether solvent or a mixed solvent of the chain ether solvent and an aromatic hydrocarbon solvent.
However, since the above conventional processes use the chain ether solvent having a relatively low boiling point, such as diethyl ether, the reaction system must be cooled. Thus, to produce the (fluoroaryl)borane compound for industrial use, a cooling apparatus or the like is indispensable. Moreover, diethyl ether is highly inflammable. In addition, in the above conventional processes, it is difficult to control the reaction and a by-product, such as a quaternary compound of boron such as a tetrakis(fluoroaryl)borate derivative, is produced. This makes it difficult to selectively obtain the (fluoroaryl)borane compound, such as tris(fluoroaryl)borane and bis(fluoroaryl)boryl halide. Furthermore, the chain ether solvent is expensive compared with a cyclic ether solvent.
Thus, the above conventional processes have a problem that they are not readily applied for industrial use. In other words, not only are the solvents difficult to handle, but also the (fluoroaryl)borane compound, such as tris(fluoroaryl)borane and bis(fluoroaryl)boryl halide, can not be produced selectively at a low cost in a simple manner. Using a cyclic ether solvent in the above conventional processes can trigger a side-reaction, such as a ring-opening polymerization of the cyclic ether solvent. In addition, using an aromatic hydrocarbon solvent alone in the above conventional processes can reduce the yield of the (fluoroaryl)borane compound, such as tris(fluoroaryl)borane and bis(fluoroaryl)boryl halide.
Therefore, to solve the above problem, the present invention has a second object to provide a process of producing a (fluoroaryl)borane compound, such as tris(fluoroaryl)borane and bis(fluoroaryl)boryl halide, selectively at a low cost in a simple manner.